The entire disclosure of Japanese Patent Application No. 2007-005464, filed Jan. 15, 2007 is expressly incorporated herein by reference.
1. Technical Field
The present invention relates to a technique for embedding invisible information in images.
2. Related Art
A variety of techniques have been developed for embedding invisible information in images. For example, Japanese Patent No. JP-A-2005-249968 discloses a technique for embedding a specific type of information that is visible only by using infrared radiation, which is achieved by printing the images with a special toner that is sensitive to infrared light. In another example known in the related art which is described in Japanese Patent No. JP-A-2001-191565, the invisible information is embedded by making the smoothness of one area of specially coated paper different from another area of the paper by applying a heat treatment to the specified area.
One disadvantage of the methods of the related art, however, is the methods are not user-friendly. For example, the first example of the related art described with reference to Japanese Patent No. JP-A-2005-249968, the method requires a special toner for embedding the invisible information into the images. In addition, the technique further requires a dedicated infrared scanning apparatus for reading out the embedded invisible information. In the second example of the prior art described with reference to Japanese Patent No. JP-A-2001-191565 also requires a special type of paper that is capable of changing its surface status when a heat treatment is applied thereto. Thus, as described above, the known techniques for handling invisible information require special dedicated apparatuses or the like, meaning that it is difficult for a user to create invisible information into images that may be subsequently read.